1. Field of the Invention
The present invention relates to gelatinized microcapsules for magnetic display in which a dispersion medium, magnetic powder and nonmagnetic powder are enclosed.
2. Description of the Prior Art
Many methods of magnetic display are well known to date; for example, a magnetic display method that makes small rooms between two plates, seals ball-shaped magnetic powder and tungsten oxides particles in liquid in the small rooms and makes a display by moving the magnetic powder to the surface by magnetic force (So-called as moving type as noted below) was published in Japanese Patent Publication Kokoku S51-10959. Furthermore, inventions published in Japanese Patent Publication Kokoku S57-27463, S59-31710, S59-47676 and S62-53359 have made an improvement of the dispersion medium in order to afford a good dispersion of the magnetic powder and the tungsten oxide particles. Among them, there is an invention concerning a magnetic display system in practical use that makes small rooms with a size of 4 mm.sup.3, having honeycomb shape on a supporting plate, injects liquid having a white pigment and magnetic powder therein in the honeycombs and laminates and seals a transparent sheet on it to finish it. According to this display system, a display may be made by scanning a magnet on the back surface of the magnetic display plate from one side to the opposite so as to attract the magnetic powder in the honeycombs to the back surface and to make the surface white. While making contact using a permanent magnetic pen with the surface of the magnetic display, the magnetic powder in the contact part moves to the surface and image appears.
On the other hand, in Publication of Japanese Patent Publication Kokoku S54-29895, a magnetic record medium that is produced by coating microcapsules having sensitive flakes in it that have sensitivity to a magnetic field and are floating in a liquid on a base plate is described. According to this invention, when a magnetic field is brought to bear on the magnetic record medium, the sensitive flakes in the microcapsules are oriented in a perpendicular direction, only a part of the sensitive flakes is under the magnetic field, moves in longitudinal direction, orients to horizontal to the magnetic record medium and shows an image (so-called as deflection type as below). The same magnetic display method using the magnetic flakes are also published in a Publication of Japanese Patent Application Laid-open S63-153197, S64-19384 and H1-145637. The two types of moving type and deflection type are also published in a Publication of Japanese Patent Publication Kokoku S55-29880. In the magnetic display system using ball-shaped magnetic powder, an invention according to which a better display may be made by specifying the size of microcapsules and mixing two kinds of microcapsules of different sizes is described in Japanese Patent Publication Kokoku H4-233581.
There are some problems among the inventions published to date, particularly in Japanese Patent Publication Kokoku H4-233581. The magnetic display method by using microcapsules consisting of the ball-shaped magnetic powder in it can not be put into practical use, because although a good display may be made, the images are not clear and the recording speed and erasing speed are slow when the magnetic force is weak.
Further, the microcapsule particles may be destroyed gradually while writing repeatedly by a magnetic pen and clearness of the display sheet diminishes. Durability of the display sheet has to be improved.
Therefore, the inventors of the invention have conducted many researches and discovered that the durability of microcapsule magnetic display sheet depends on the thickness and hardness of the transparent film and the arrangement of a cushion element (pressure-proofing film) adjacent to the microcapsule dispersoid and the destruction of the microcapsules caused by pressure is relieved by the thickness and hardness of the transparent film. The inventions have been accomplished based on the discoveries mentioned above.